On Fri, Aug 11, 2017 at 06:00:20PM -0700, Tom Herbert wrote: > On Thu, Aug 10, 2017 at 12:13 PM, Shaohua Li <s...@kernel.org> wrote: > > On Thu, Aug 10, 2017 at 11:30:51AM -0700, Tom Herbert wrote: > >> On Thu, Aug 10, 2017 at 9:30 AM, Shaohua Li <s...@kernel.org> wrote: > >> > On Wed, Aug 09, 2017 at 09:40:08AM -0700, Tom Herbert wrote: > >> >> On Mon, Jul 31, 2017 at 3:19 PM, Shaohua Li <s...@kernel.org> wrote: > >> >> > From: Shaohua Li <s...@fb.com> > >> >> > > >> >> > Please see below tcpdump output: > >> >> > 21:00:48.109122 IP6 (flowlabel 0x43304, hlim 64, next-header TCP (6) > >> >> > payload length: 40) fec0::5054:ff:fe12:3456.55804 > > >> >> > fec0::5054:ff:fe12:3456.5555: Flags [S], cksum 0x0529 (incorrect -> > >> >> > 0xf56c), seq 3282214508, win 43690, options [mss 65476,sackOK,TS val > >> >> > 2500903437 ecr 0,nop,wscale 7], length 0 > >> >> > 21:00:48.109381 IP6 (flowlabel 0xd827f, hlim 64, next-header TCP (6) > >> >> > payload length: 40) fec0::5054:ff:fe12:3456.5555 > > >> >> > fec0::5054:ff:fe12:3456.55804: Flags [S.], cksum 0x0529 (incorrect -> > >> >> > 0x49ad), seq 1923801573, ack 3282214509, win 43690, options [mss > >> >> > 65476,sackOK,TS val 2500903437 ecr 2500903437,nop,wscale 7], length 0 > >> >> > 21:00:48.109548 IP6 (flowlabel 0x43304, hlim 64, next-header TCP (6) > >> >> > payload length: 32) fec0::5054:ff:fe12:3456.55804 > > >> >> > fec0::5054:ff:fe12:3456.5555: Flags [.], cksum 0x0521 (incorrect -> > >> >> > 0x1bdf), seq 1, ack 1, win 342, options [nop,nop,TS val 2500903437 > >> >> > ecr 2500903437], length 0 > >> >> > 21:00:48.109823 IP6 (flowlabel 0x43304, hlim 64, next-header TCP (6) > >> >> > payload length: 62) fec0::5054:ff:fe12:3456.55804 > > >> >> > fec0::5054:ff:fe12:3456.5555: Flags [P.], cksum 0x053f (incorrect -> > >> >> > 0xb8b1), seq 1:31, ack 1, win 342, options [nop,nop,TS val 2500903437 > >> >> > ecr 2500903437], length 30 > >> >> > 21:00:48.109910 IP6 (flowlabel 0xd827f, hlim 64, next-header TCP (6) > >> >> > payload length: 32) fec0::5054:ff:fe12:3456.5555 > > >> >> > fec0::5054:ff:fe12:3456.55804: Flags [.], cksum 0x0521 (incorrect -> > >> >> > 0x1bc1), seq 1, ack 31, win 342, options [nop,nop,TS val 2500903437 > >> >> > ecr 2500903437], length 0 > >> >> > 21:00:48.110043 IP6 (flowlabel 0xd827f, hlim 64, next-header TCP (6) > >> >> > payload length: 56) fec0::5054:ff:fe12:3456.5555 > > >> >> > fec0::5054:ff:fe12:3456.55804: Flags [P.], cksum 0x0539 (incorrect -> > >> >> > 0xb726), seq 1:25, ack 31, win 342, options [nop,nop,TS val > >> >> > 2500903438 ecr 2500903437], length 24 > >> >> > 21:00:48.110173 IP6 (flowlabel 0x43304, hlim 64, next-header TCP (6) > >> >> > payload length: 32) fec0::5054:ff:fe12:3456.55804 > > >> >> > fec0::5054:ff:fe12:3456.5555: Flags [.], cksum 0x0521 (incorrect -> > >> >> > 0x1ba7), seq 31, ack 25, win 342, options [nop,nop,TS val 2500903438 > >> >> > ecr 2500903438], length 0 > >> >> > 21:00:48.110211 IP6 (flowlabel 0xd827f, hlim 64, next-header TCP (6) > >> >> > payload length: 32) fec0::5054:ff:fe12:3456.5555 > > >> >> > fec0::5054:ff:fe12:3456.55804: Flags [F.], cksum 0x0521 (incorrect -> > >> >> > 0x1ba7), seq 25, ack 31, win 342, options [nop,nop,TS val 2500903438 > >> >> > ecr 2500903437], length 0 > >> >> > 21:00:48.151099 IP6 (flowlabel 0x43304, hlim 64, next-header TCP (6) > >> >> > payload length: 32) fec0::5054:ff:fe12:3456.55804 > > >> >> > fec0::5054:ff:fe12:3456.5555: Flags [.], cksum 0x0521 (incorrect -> > >> >> > 0x1ba6), seq 31, ack 26, win 342, options [nop,nop,TS val 2500903438 > >> >> > ecr 2500903438], length 0 > >> >> > 21:00:49.110524 IP6 (flowlabel 0x43304, hlim 64, next-header TCP (6) > >> >> > payload length: 56) fec0::5054:ff:fe12:3456.55804 > > >> >> > fec0::5054:ff:fe12:3456.5555: Flags [P.], cksum 0x0539 (incorrect -> > >> >> > 0xb324), seq 31:55, ack 26, win 342, options [nop,nop,TS val > >> >> > 2500904438 ecr 2500903438], length 24 > >> >> > 21:00:49.110637 IP6 (flowlabel 0xb34d5, hlim 64, next-header TCP (6) > >> >> > payload length: 20) fec0::5054:ff:fe12:3456.5555 > > >> >> > fec0::5054:ff:fe12:3456.55804: Flags [R], cksum 0x0515 (incorrect -> > >> >> > 0x668c), seq 1923801599, win 0, length 0 > >> >> > > >> >> > The flowlabel of reset packet (0xb34d5) and flowlabel of normal packet > >> >> > (0xd827f) are different. This causes our router doesn't correctly > >> >> > close tcp > >> >> > connection. The patches try to fix the issue. > >> >> > > >> >> Shaohua, > >> >> > >> >> Can you give some more detail about what the router doesn't close the > >> >> TCP connection means? I'm guessing the problem is either: 1) the > >> >> router is maintaining connection state that includes the flow label in > >> >> a connection tuple. 2) some router in the path is maintaining > >> >> connection state, but when the flow label changes the flow's packet > >> >> are routed through a different router that doesn't have a state for > >> >> the flow it drops the packet. #1 should be easily fix in the router, > >> >> flow labels cannot be used as state. #2 is the known problem that > >> >> stateful firewalls have killed our ability to use multihoming. > >> > > >> > The #2 is exactly the problem we saw. > >> > > >> >> Another consideration is that sk_txhash is also used in routing > >> >> decisions by the local host (flow label is normally derived from > >> >> txhash). If you want to ensure that connections are routed > >> >> consistently for timewait state you might need sk_txhash saved also. > >> > > >> > As far as I understood, we don't use sk_txhash for routing selection. > >> > The code > >> > does routing selection with flowlabel user configured, at that time we > >> > don't > >> > derive fl6.flowlabel from skb->hash (which is from sk_txhash). The code > >> > always > >> > does routing selection first and then uses ip6_make_flowlabel to build > >> > packet > >> > data where we derive flowlabel from skb->hash. > >> > > >> That is assuming one particular use case. Generally, if you want to > >> ensure all packets for a flow take the same path you'll need tx_hash > >> and make it persistent (disable flow bender). For instance, if you > >> were doing UDP encapsulation like in VXLAN the UDP source port > >> selection is unaffected by saved flow label for the lifetime of the > >> flow. So we would still hit #2 in that case and the stateful device > >> doesn't see whole flow. It might be just as easy to move tx_hash in > >> skc_common so that it's available in TW state for this purpose. Then > >> when moving to TW state just copy the tx_hash. > > > > Hi Tom, > > > > My original implementation is to add a tx_hash in tw sock, we then copy > > sock's > > tx_hash to the tw tx_hash. This does makes things simplier. One concern from > > Eric is this will increase the size of tw sock. If we move tx_hash to > > skc_common, all sock size will increase, is this acceptable? > > I think that can only be measured by how critical it is to > persistently route all packets the same exact way for every > connection. Page one of the IP book clearly states that IP packets can > be dropped, duplicated, or received out of order. Received OOO implies > that packet for the same flow are allowed to take different paths. The > requirement that packets for the same flow must always take the same > path through the network was created by stateful middleboxes-- it's > not inherent in the architecture of IP networking. Unfortunately, > we're seeing this become more and more of a problem as more devices > are multi-homed (like smart phones) and these network requirement > cripple our ability to take advantage of features like that. > > Personally, I wish the middleboxes fix the problem they created, but I > suppose we need to be pragmatic at least in the short term.
Hmm, I still hesitate to add a new field in skc_common. Fixing current problem looks propriate in current stage. I'd defer fixing the generic issue till it's necessary. Thanks, Shaohua
